It is known to amplify a signal by converting such signal to a pulse-width modulated (PWM) signal and thereafter to convert the PWM signal to an amplified signal by utilizing the PWM signal to sample a linear ramp. The duty cycle of the PWM signal is dependent upon the amplitude of the input signal and the value of the output signal is subsequently dependent upon this duty cycle.
This is a two stage process carried out in a two stage circuit. The first stage of such an amplifier compares the voltage value of the input signal with a first linear voltage ramp which swings from a first, or low, amplitude value to a second, or high, amplitude value. For the duration that the ramp voltage is lower than the input signal voltage, the amplitude of the PWM signal is conditioned to be high. When the voltage of the ramp signal exceeds the voltage of the input signal, the PWM signal is conditioned to be low.
The second stage of the amplifier compares the PWM signal with a second linear ramp signal with a predetermined dv/dt or slope, e.g., from low to high. The PWM signal samples the second ramp signal at the high-to-low transition of the PWM signal and thereby generates the output voltage with a value which depends on the duty cycle of the PWM signal.
It is known to utilize the aforementioned type of amplifying apparatus to apply a video signal to the column busses of liquid crystal display (LCD) devices. In such devices a driven LCD pixel changes its reflectivity or transparency respectively responsive to the value of the video output signal.